1. Field of the Invention
This invention relates to obtaining of a chopped, combustible mixture from municipal solid waste, and, more particularly, to a substantially plastic-free, low ash content and low sulfur content fuel, and the apparatus and process of obtaining that fuel product.
2. Description of the Prior Art
Attempts have been made to treat municipal solid waste garbage, particularly to separate or classify the material content, chop the content of the solid waste into relatively small particle size, classify and separate the material content into ferrous metal, non-ferrous metal, glass, grit, sand, textile, plastic and paper components. It has been found that municipal solid waste contains a high content of combustible material permitting the municipal solid waste to function as a fuel having a relatively high BTU content, particularly where that fuel is added as a secondary fuel to a primary fuel, such as a hydrocarbon fuel, for fueling commercial boilers, electrical generating plants, commercial and industrial heating plants and the like.
In the treatment of municipal solid wastes, various types of mechanical machines are employed to break the bulky municipal solid waste trash into smaller sizes and to attempt separations of the material content, particularly to remove large quantities of particles, such as glass and dirt as well as to separate the components of such municipal solid waste such that the components may be re-employed as pulp in the manufacture of various products. Thus, it is possible to recycle much of the material appearing in municipal solid waste refuse. A process and apparatus for the dry recovery and restoration of confetti thrashed paper, construction aggregates, fibrous fuel and other materials from solid municipal refuse forms a subject matter of my earlier U.S. Pat. No. 4,072,273.
In that patent application, municipal solid waste in an automatic apparatus is chopped, sorted, air cleaned, subjected to specific gravity and ballistic separation while separating and rejecting loose, soft, decayed, wet and extraneous matter, including high-density particles and abrasive material such as non-ferrous metal, grit and glass. One part of that apparatus which is highly useful in further chopping and ballistic separation of the particle content of the municipal solid waste comprises a vertically-oriented cylindrical rotor chamber. An opening in the upper end receives previously chopped, ferrous metal-free, municipal solid waste mixture in a vertically-oriented single rotor mounted for rotation about its axis within the chamber, and a plurality of radially extending hammer blades chop the mixture and impart centrifugal force to the mixture particles for ballistic separation by forcing the particles of given size to pass through a cylindrical classifier screen concentrically surrounding the rotor blades and positioned within the rotor chamber and being spaced slightly from the tips of the blades to permit the radial passage of the particles corresponding to the screen mesh size. Those chopped mixture particles which, because of weight and/or size, do not pass through the classifier screen fall by gravity from the bottom of the rotor chamber. Normally, the specific gravity and ballistic separation achieves a contaminated confetti thrashed paper at the bottom end of the rotor chamber, and the extraneous matter such as high-density metal particles and abrasive materials are separated horizontally by passage through the classifier screen. While this type of ballistic separation provides satisfactory operation in terms of further chopping and thrashing the refuse particles, it has not performed adequately to insure separations of any desired degree for oversized contaminants from the usable particle material.
Particularly, this type of machine, although capable of providing, by way of specific gravity and centrifugal force, classification and separation of some contaminant particles from the confetti thrashed paper has been incapable of achieving separation of the chopped plastic film and other lightweight plastic particles from the confetti thrashed paper and the contaminants. This has resulted in classified products which cannot normally be employed as an adequate source of fuel since, on the one hand, the products include excessive amounts of high-density particles, such as pulverized glass, ceramics, grit, hard plastic and non-ferrous metal, whereby the ash content after combustion is well above accepted limits while, on the other hand, the presence of heavy plastic bags, particularly plastic film and bottles do not provide a thoroughly chopped fuel product.
Further, because of the plastics and diverse contamination of the prior art confetti, subsequent to the specific gravity and ballistic classifying, it was necessary to subject the confetti thrashed paper of my prior application to subsequent steam digester treatments to affect digestion of that mixture into fiber pulp, at which time the resulting pulp was later air classified, permitting the then plastic-free fiber to be subsequently used for recycled paper pulp or as a fuel product.
It is therefore a primary object of the present invention to provide an improved apparatus for use in the treating of raw materials of diverse nature and from various sources, including organics and inorganics, specifically for city garbage, yard trash and refuse having no commercial value, in which portions of the materials are fragmentized, selected in accordance with material content and size, resulting in select products of low resultant ash content and of low plastic film content, for example, as a uniform refuse fuel product for generaing industrial heat and electric power.
It is a further object of the present invention to provide within a single apparaus processes which effectively treat the raw feed materials within four zones, including two axially spaced screen selectifier zones, an intermediate solution treating zone and a final high-velocity aspiration zone, and to aspirate lightweight plastic films, textiles and the like out of the screen selectifier zone and facilitate utilization of recovery materials upstream of the aspiration zone.
It is a further object of the present invention to provide an apparatus employing independent rotors cooperating with cylindrical screens at spaced vertical positions within a vertical chamber while effecting directed airflows at relatively high velocities and within a venturi which opens to the rotor zone to facilitate discharge operations including separations of lightweight plastics for full recovery purposes.
It is a further object of the present invention to provide an improved process for treating municipal solid waste garbage to render said refuse into an essentially low ash content chopped mixed fuel product resulting therefrom, with the fuel product ash content consistently below 3% and having a heating value of approximately 7,300 BUT per pound.
It is a further object of this invention to provide an improved apparatus in the form of a high-speed rotor carrying radial rotor blades and rotating within concentric selectifier screens, and wherein the unique rotor includes air passages between the rotor blades to create directed airflow from the center of the rotors outwardly through the screen to assist in clearing the screen plates from dust and airborne particles through the introduction of pulsating airflows on the screen.